Friday, September 22, 2017

Tree of the Week: Sweet Gum (Liquidambar styraciflua)

Today is the first day of autumn. There are a few trees in the arboretum that are showing their fall colors. The standout specimen is an old sweet gum (Liquidambar styraciflua). If you are passing through the arboretum, you might notice a few of its brilliant alizarin leaves on the ground.

Currently, there are two sweet gums in the arboretum collection. The youngest of the two was added this summer. It's camouflaged in a groundsel bush (Baccharis halimifolia), growing on the grassy slope north of Cline Hall. The senior tree is an on-site native, age unknown. It has been growing along the drainage on the south side of the arboretum for a long time. This old tree has withstood a great deal of abuse over the years. According to Ed Leuck's log, the sweet gum was decapitated by the tornado of Easter Sunday, 1999, and the top was further damaged a year later. It also survived the construction of the Fitness Center and the necessary sidewalk installations. Today, the tree looks healthy overall, but we will need to keep an eye on the trunk of the tree, as it appears to be exhibiting signs of bleeding necrosis. 

Note: The photos below were taken shortly after noon on a mostly cloudy day. It has been hot, humid and cloudy during the last week of summer.

The sweet gum stands directly behind the arboretum sign. Next in line, behind the sweet gum, is the narrow drainage channel that runs north-to-south through the arboretum.

Stepping back, towards Mickle Hall, we can see that the sweet gum is at the bottom of a steep slope. Looking up, we can see that the leaves are changing colors.

Right now we have green, light-green, yellow, orange and some red as well.
In this photo, taken on the north side of Cline Hall, the crown of the sweet gum is seen from a distance, wedged between the dark green foliage of a magnolia and an oak. In the foreground, Magnolia grandiflora (covered in Berchemia scandens) stands on the left, and Quercus texana stands on the right.
The star-shaped leaves turn beautiful colors in the fall. This is a vibrant crimson leaf, but you can find yellow and orange leaves, too.
Sweet gum balls from last year are still in the leaf litter. The gum balls can be a nuisance when they drop because our old sweet gum tree grows at the intersection of two high-traffic sidewalks. Our new addition to the collection, the young volunteer, is growing in the middle of a grassy slope, so its fruits won't cause as many problems. 
Old and new spiny fruits of the sweet gum tree
The mature sweet gum has gray, rough bark. To the left of the tree we can see bright red seeds of the strawberry bush (Euonymus americanus).

For more information about this species consult the following:
University of Florida IFAS Extension
NC State University
United States Department of Agriculture
Louisiana Plant Identification and Interactive Virtual Tours

Thursday, September 14, 2017

Tree of the Week: Bur Oak (Quercus macrocarpa)

The autumnal equinox is next week, marking an end to summer. The cooler weather over the past week has signaled the coming change in seasons. With plenty of cloud coverage and a nice breeze, we haven't been desperate for shade. So, with the end of summer so goes too our discussion of shade trees. The last entry for 2017 in this series is the bur oak (Quercus macrocarpa).

There are two bur oaks in the arboretum collection. Both are over twenty years old and both provide a good amount of shade on the eastern clay slope of the arboretum. The images below are from the older of the two trees. This bur oak was purchased from Home Depot and planted in October 1993. It is of interest this week because of its curiously large acorns. It's hard to say if the cap of the acorn more closely resembles the Scottish tam, the Russian ushanka (ear-flaps tied up), or the Caucasian papakha.

All photos below were taken shortly before noon on a mostly cloudy day.

The bur oak is pictured above in the foreground, with a Shumard oak (Quercus shumardii) directly behind it. The Shumard is a few years older and has an obviously thicker trunk. The two compete for sunlight on this eastern clay slope, shading the gravel path during the heat of the day.
The bur oak is pictured front and center, with a long-leaf pine (Pinus palustris) and French mulberry bushes (Callicarpa americana) closer to the brick wall.
Approximately 25 years-old, this bur oak is already providing a good amount of shade.
The underside of the lobed leaf (quite large) is light green and hairy to the touch. 
The branches of the bur oak have corky ridges similar to those seen on the bark of the winged elm (Ulmus alata) and the sweetgum tree (Liquidambar styraciflua).
The bur oak is known for its large fruit and unique cap.
This acorn, cap included, measures more than 1.5 inches.
By comparison, the water oak (Quercus nigra) acorns are very small.
The dark green leaves of the bur oak are large; this leaf blade is 8 inches long.
Rough, shaggy bark of the bur oak (Quercus macrocarpa)


You can see more pictures of the arboretum's bur oaks here.



For more information about this species consult the following:
University of Florida IFAS Extension
United States Department of Agriculture 
The Ohio State University

Sunday, September 10, 2017

Tree of the Week: Hercules' Club (Aralia spinosa)

The Hercules' club (Aralia spinosa), our tree of the week, is especially noteworthy right now: its large fruit clusters are providing local birds a late summer snack.  

We have two groupings of Hercules' club in the arboretum. In 1989, Nick Leuck gathered Hercules' club seeds from Caney Lake, in Grant Parish. Those seeds were planted in the arboretum on the hill that slopes down from Hamilton Hall, where they successfully grew. A decade later, in the fall of 1999, two shoots were removed and replanted at the southwest corner of the lower pond. Today, only one young shoot remains at the original planting location, while approximately 20 shoots can be counted at the second location. Although the pond feature has since been removed, the area remains wet for a considerable part of the year, making it possible for the Hercules' club to thrive. In fact, it has been so successful there that overcrowding has become a problem over the past several years; removal of new trees has been necessary.
The photo above was taken at noon on a mostly sunny day. Dappled sun is hitting the grass and sidewalk, but the area under the Hercules' clubs (pictured to the left of the sidewalk) is densely shaded. This is a low area that often stays wet; this species seems to love it and new trees sprout there each year.
Of the approximately 20 individual trees, only a few of the tallest trees have fruit cluster, and they are out of arms' reach for humans.
This is only a section of a very large, bipinnately compound leaf.

This leaf was taken from one of the smaller Hercules' clubs. The leaf is approximately 26 inches in length. Leaves are much, much larger on the taller trees. 
Leaflets of the Hercules' club have serrated edges, and notice the little spines near the leaflet.
A ladder is needed to closely observe the fruit clusters.
Fruits of the Hercules' club are small, black drupes.
Numerous spines can be seen (and felt) along the trunk of the tree, giving it a threatening appearance, hence the origin of the common name 'Hercules' club'. Should a hydra appear in the arboretum, we would be well equipped to subdue it.
Detail of spines
This is bark from one of the largest Hercules' clubs. The spines are less noticeable, but still painful.


You can see additional pictures of the arboretum's Hercules' club here.

Check out the following links for more information about this species:
United States Department of Agriculture
Louisiana Plant Identification and Interactive Virtual Tours (LSU AgCenter)
University of Florida
NC State University

Saturday, September 2, 2017

This past Wednesday a lot of rain fell, accompanied by some gusts of wind. A couple large, dead branches were knocked loose and fell to the ground with the rain. Luckily for us, some branchlets fell, too, giving us a look at this year's growth from the tip-top of the old trees. 

White oak (Quercus alba) leaves and acorns
This bristly fruit fell from the hybrid American chestnut tree (Castanea dentata). Ouch! We aren't going to bust it open quite yet.
Water oak (Quercus nigra) acorn and leaves.
The sweetgum (Liquidambar styraciflua) often acquires a bad wrap because of its pointy fruits. There is one large on-site native sweetgum in the arboretum collection, and, admittedly it does make a mess of the sidewalks. It has sustained damage over the years, so this past summer a volunteer sweetgum growing up in the groundsel bush (Baccharis halimifolia), away from foot traffic, was admitted into the catalogue, so that we have a back-up specimen should something happen to the old one.
This image shows the relative size of the different fruits.
The fruit pods of the strawberry bush (Euonymus americanus) are changing color and opening up.
The orange-red seeds of the strawberry bush are revealed. They should not be eaten!


Tree of the Week: Water Tupelo (Nyssa aquatica)

The sun is shining in Shreveport this weekend. The remnants of Hurricane Harvey brought heavy cloud coverage in the early part of last week and steady rain on Wednesday. Thursday, things cleared up, and on Friday the sun steamed everything up. If you're outside enjoying the late summer weather, you might also be looking for a spot of shade.

There are many beautiful shady spots on Centenary's campus, and if you're in the arboretum, take time to appreciate the water tupelo (Nyssa aquatica), shading the long white wooden bridge. It was purchased from Woodlanders nursery (Aiken, S.C.) and added to the arboretum collection in October 1988, making it more than 30-years-old. Currently, it is doing very well, despite competition, and littering the wooden bridge with its fruits. 
 
The long white wooden bridge in the arboretum is mostly shaded, with only some dappled sunlight hitting the planks. In this picture, we are looking east, and our tree of the week is pictured to the left of the bridge, growing on its north side.

The water tupelo (the center-most tree in the above photograph) grows in a very wet area. It is in competition with other water-loving trees. Immediately to the left of the water tupelo, we have a pond cypress (Taxodium ascendens). In the background, at the far left, we have a bald cypress (Taxodium distichum).  

This water tupelo is competing for sunlight. Its primary competitor is the pond cypress (Taxodium ascendens), planted a year after the tupelo. The competition might explain the crook in the tupelo's trunk.

There are a lot of fruits on the tree this year.
The elliptic leaf has smooth, wavy edges and a pointed tip.
The numerous speckled drupes blend in with the worn wooden planks.
The off-white background offers a better look at the oblong shape of the fruit.
There are significant accumulations of green fruits on the ground under the tree, and some of the fruits appear to have been gnawed on (lets blame the squirrels). There are also a few patches of sensitive fern (Onoclea sensibilis) growing in the shade of this water tupelo. The fern, which was originally collected from the Caroline Dormon Nature Preserve, is pictured in the bottom left hand corner.
The bark of this tree, which is more than 30-years-old, is deeply furrowed. The trunk shows some characteristic swelling.

For more information about this species consult the following:
Arkansas Agriculture Department (Great picture of old water tupelo!)
Louisiana Plant Identification and Interactive Virtual Tours (LSU AgCenter) 
USDA Forest Service 

Sunday, August 27, 2017

Summer Update: Fruits and Flowers

There are a handful of immature fruits on the strawberry bush (Euonymus americanus), growing in the shade of our on-site native sweetgum (Liquidambar styraciflua). When the capsules open, they should reveal bright red seeds (do NOT eat).
The drupes of the Georgia holly (Ilex longipes) are ripening.
We have been watching the Mexican plums (Prunus mexicana) this summer. Numerous fruits fell early, but the branches are still heavy with ripening plums.
The fruits of the arrowwood bushes (Viburnum dentatum) are almost black.
Here we have a newborn Gulf fritillary caterpillar conveniently stationed on its obligatory food source: the yellow passion flower vine (Passiflora lutea). The vine isn't long for this world.
The creeping cucumber vine (Melothria pendula) is producing fruits that you do not taste as good as they look. (do NOT eat)
In the arboretum collection, we have two kinds of French mulberry (Callicarpa americana). One produces purple berries, the other produces white berries. Above, we have an individual that produces the white variety--these berries won't turn purple.
The Louisiana catchfly (Silene subciliata) may not actually catch flies, but it certainly does catch the eye! They provide a bold dash of color in the late summer landscape. This nice patch is growing under a white oak (Quercus alba).